Simulating the impact of an AMOC weakening on the Antarctic Ice Sheet using a coupled climate and ice-sheet model

Climate model studies show that a shutdown of the Atlantic Meridional Overturning Circulation (AMOC) reduces northward heat transport into the North Atlantic, which causes an accumulation of heat in the South Atlantic Ocean. The Antarctic Ice Sheet meanwhile has been shown to be particularly susceptible to temperature changes in ocean water flowing into the cavities near ice-shelf grounding lines. How AMOC-induced modulation of inter-hemispheric heat transport could influence the present-day state of the Antarctic Ice Sheet via a southward propagation of warm anomalies is little studied. However, interactions between AMOC and the West Antarctic Ice Sheet are highly relevant, because both systems are classified as climate tipping elements, which can trigger irreversible changes in the Earth system. In this study we simulate a shutdown of the AMOC, induced by artificial freshwater input to the North Atlantic, in a global climate model interactively coupled to an ice-sheet model for Antarctica. In line with previous studies, an AMOC shutdown causes increased sea-surface temperatures in the Southern Hemisphere along with a small shift in the mid-latitude westerlies. However, Southern Ocean subsurface temperatures, which drive basal melt in Antarctica, do not change in most regions along the Antarctic margin for the first eight centuries post AMOC shut down. Therefore, we do not find a change in the total Antarctic Ice volume in this time span. At later times, this is followed by a shift towards stronger Ross Sea convection, causing negative subsurface temperature anomalies of −1.4 °C on average. This cooling decreases basal melt in Antarctica, however increased calving balances the ice mass change. Even though our approach is simplified as the coupling is limited to the ocean-ice interface and results might be partly impacted by artificial freshwater hosing/forcing, this study is an important first step to quantitatively investigate Earth-system stability across both hemispheres in coupled climate–ice-sheet models.